The long-term goal is to determine the mechanism by which part or all of a newly-formed chain of nuclear RNA is degraded, and to test whether the level of such degradation can limit the growth rate of normal or viral-transformed cells. Some leads from our earlier work on processing reactions in E. coli are being followed up with HeLa cells -for example, functions of a nuclease that cleaves E. coli rRNA precursors at specific double-stranded sites (RNase III) are being examined with corresponding material from HeLa cells, and studies of the nucleolar and nucleoplasmic RNases of HeLa cells are being continued. In addition, rigorous experiments to quantitate the precise rates of turnover of various RNA species in the nucleus are in progress with HeLa cells, and will be extended to non-growing, normally growing, and SV40-transformed human fibroblasts.